Details of former national security advisor John Bolton’s unpublished book manuscript became public Sunday.These details suggested that Bolton could provide firsthand evidence that President Trump directly tried to deny security assistance to Ukraine until they announced investigations into political opponents, including Joe and Hunter Biden. That assertion from Bolton’s book has renewed the call by Democrats for witnesses in Trump’s Senate impeachment trial.And yet, that interaction between Trump and Bolton, though potentially the most explosive, wasn’t the only conversation alleged in the leaked details of Bolton’s book. Another, was a key interaction between Bolton and Attorney General William Barr shortly after Trump’s now infamous call with Ukraine president Volodymyr Zelensky.On this episode Matt Zapotosky, The Post’s Justice Department reporter, focuses on that Bolton-Barr conversation: What the purported exchange between Bolton and Barr might tells us about the Attorney General’s role in Ukraine-related events, where it leaves a Justice Department designed to maintain independence from the president and uphold the rule of law, and of course what it all means for Trump’s impeachment trial.Related episodes:How does Attorney General Barr view presidential power?Block witnesses? Allow evidence? The battles ahead for the Senate impeachment trial Congress wants to hear from John Bolton. What might he tell them?